It is common practice for formulators of cleaning compositions to include, in addition to a cleaning active material, a builder to remove hardness cations (e.g. calcium cations and magnesium cations) from washing solution which would otherwise reduce the efficiency of the cleaning active material (e.g. surfactant) and render certain soils more difficult to remove. For example, laundry detergent compositions typically contain an anionic surfactant and a builder to reduce the effects of hardness cations in wash solutions. In this context, the builder sequesters or "ties up" the hardness cations so as to prevent them from hindering the cleaning action of the anionic surfactant in the detergent composition.
As is well known, water-soluble phosphate materials have been used extensively as detergency builders. However for a variety of reasons, including eutrophication of surface waters allegedly caused by phosphates, there has been a desire to use other builder materials in many geographic areas. Other known builders include water-soluble builder salts, such as sodium carbonate, which can form precipitates with the hardness cations found in washing solutions. Unfortunately, the use of such builders alone does not reduce the level of hardness cations at a sufficiently rapid rate. For practical purposes, the acceptable level is not reached within the limited time required for the desired application, e.g. within 10 to 12 minutes for fabric laundering operations in North America and Japan.
Moreover, some of these water-soluble builder salts, while attractive from the point of view of cost, have several disadvantages, among which are the tendency of the precipitates formed in aqueous washing solutions (e.g. insoluble calcium carbonate) to become deposited on fabrics or other articles to be cleaned. One alleged solution to this problem has been to include a water-insoluble material which would act as a "seed crystal" for the precipitate (i.e. calcium carbonate). Of the many materials suggested for such use, very small particle size calcite has been the most popular.
However, the inclusion of calcite in detergent compositions has been problematic because of the sensitivity of the hardness cation/salt anion (e.g. calcium/carbonate) reaction product to poisoning by materials (e.g. polyacrylate or certain anionic surfactants) which may be present in the washing solution. Without being limited by theory, the poisoning problem prevents the reaction product from forming in that crystallization onto the seed crystal is inhibited. Consequently, calcite typically has to be produced in a very small particle size in order to have a larger surface area which is harder to poison. This, however, renders the very small calcite particle dusty and difficult to handle. Moreover, the required particle sizes are so small (at least having 15 m.sup.2 /g or more of surface area) that manufacturing of such calcite particles is extremely expensive. For example, production of such small calcite particles may require a controlled "growing" process which is extremely expensive. Another problem associated with the use of calcite as a "seed crystal" for the poisons and precipitates in washing solutions is the difficulty experienced in adequately dispersing the calcite in the washing solution so that it does not deposit on fabrics or articles which have been subjected to cleaning operations. Such deposits or residues are extremely undesirable for most any cleaning operation, especially in fabric laundering and tableware cleaning situations.
The prior art is replete with suggestions for dealing with the handling and dispersability problems associated with calcite. One previously proposed means for handling calcite is to incorporate it into a slurry, but this involves high storage and transportation costs. Another proposed option involves granulating calcite with binding and dispersing agents to ensure adequate dispersment in the wash solution. However, this option also has been difficult to implement effectively in modern day detergent compositions because the calcite granules have poor mechanical strength which continue to make them difficult to handle and process, especially when required to be very small in size. Additionally, effective binding and dispersing agents for the calcite have not been discovered to date. Specifically, most of the binding and dispersing agents proposed by the prior art are themselves poisons which reduce the "seed activity" of the calcite. Consequently, it would be desirable to have an improved inexpensive builder material which overcomes the aforementioned limitations and is easy to handle, readily dispersible in washing solutions and exhibits improved builder performance.
Accordingly, despite the aforementioned disclosures, there remains a need in the art for an inexpensive builder material for use in detergent compositions which exhibits superior performance and is less expensive to manufacture in that it does not require a very small particle size. There is also a need in the art for such a builder material which is easy to handle (i.e., is not "dusty"), easy to process and readily disperses in washing solutions.